The pair of airways, one wider, shorter and steeper than the other, formed where the windpipe forks
The main bronchi, right and left.
Anatomy · Organs & viscera
Bronchus
Main airway branch to the lungs
Thorax · respiratory system
The bronchi are the two main airways that branch from the trachea at the carina, one to each lung. Each main bronchus enters its lung at the hilum and divides into lobar bronchi (three on the right, two on the left) and then into smaller segmental bronchi. The right main bronchus is wider, shorter and more vertical than the left, which is why swallowed peanuts and other foreign bodies usually end up on the right.
How to spot them
- ▸Two tubes forming an inverted Y with the trachea, one to each lung
- ▸Cartilage plates rather than rings in the walls, which disappear in the smaller bronchioles
- ▸The right main bronchus is short (about 2.5 cm), wide and steep; the left is longer (about 5 cm), narrower and more horizontal
- ▸The left main bronchus passes under the arch of the aorta and in front of the oesophagus; the azygos vein arches over the right
What to know
The airway whose upper branch leaves before the pulmonary artery, an arrangement known as eparterial
The right main bronchus, which gives off the right upper lobe bronchus above the pulmonary artery.
The arch of the azygos vein hooks over this airway on its way to the superior vena cava
The right main bronchus, and the azygos vein.
The airway that passes below the arch of the aorta and in front of the descending aorta and oesophagus
The left main bronchus.
Three branches go to the right lung and two to the left, each supplying a lobe
The lobar (secondary) bronchi.
Airways with walls containing plates of hyaline cartilage and smooth muscle, unlike the smaller tubes beyond them
Bronchi, which lose their cartilage as they become bronchioles.
The tubes into which a peanut is most likely to slip if it is inhaled
The right main bronchus — wider, shorter and more vertical.
Key ideas
- After about 23 divisions from the trachea, the airways end in alveolar sacs. Bronchi are the first 10 or so generations, held open by cartilage; beyond them come the bronchioles.
- Smooth muscle in the walls narrows the bronchi in asthma, and drugs such as salbutamol relax it.
Quick-fire facts
- •The right main bronchus is about 2.5 cm long and the left about 5 cm long.
- •The right main bronchus makes an angle of roughly 25 degrees with the vertical, the left about 45 degrees.
- •The right lung has three lobar bronchi and 10 segmental bronchi; the left has two lobar bronchi and 8 to 10 segmental, depending on the count.
- •The azygos vein arches over the right main bronchus; the aortic arch arches over the left.
- •Inhaled foreign bodies, especially in toddlers, most often lodge in the right bronchial tree.
- •Bronchoscopy allows direct view of the carina and bronchi through a flexible tube.
- •The bronchi are lined by pseudostratified ciliated columnar epithelium with goblet cells, like the trachea.
- •Bronchitis is inflammation of the lining of the bronchi, from Greek bronkhos, meaning windpipe or throat.
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